"It's well known that the human brain accounts for about 20% of the total oxygen consumption when a person is at rest, so let us assume that the brain accounts for 20% of the total body energy consumption."

20 W

The brain makes up 2% of a person's weight. Despite this, even
at rest, the brain consumes 20% of the body's energy. The brain
consumes energy at 10 times the rate of the rest of the body per
gram of tissue. The average power consumption of a typical adult
is 100 Watts and the brain consumes 20% of this making the power
of the brain 20 W.

Glucose is the main energy source for the brain. As the size
and complexity of the brain increases, energy requirements increase.

The human brain is one of the most energy hungry organs in
the body thereby increasing its vulnerability. If the energy supply
is cut off for 10 minutes, there is permanent brain damage. There
is no other organ nearly as sensitive to changes in its energy
supply.

In 1955, Albert Einstein's brain was preserved for research.
Three scientific papers have been published examining the features
of Einstein's brain. Albert Einstein's brain differed to normal
men's brain in that his brain had more glial cells per neuron
that might indicate that neurons in Einstein's brain had an increased
"metabolic need"-- they needed and used more energy.
Einstein's brain weighed only 1,230 grams, which is less than
the average adult male brain (about 1,400 grams). The thickness
of Einstein's cerebral cortex was thinner. However, the density
of neurons in Einstein's brain was greater. In other words, Einstein
was able to pack more neurons in a given area of cortex.

The most recent study concerning Einstein's brain was published
in the British medical journal The Lancet, on June 19,
1999. They found that a portion of the brain that governs mathematical
abilities and spatial reasoning -- 2 key ingredients to the sort
of thinking Einstein did best -- was 15% wider than average allowing
better connection between its cells, which could have allowed
them to work together more efficiently.